1. Field of the Invention
The present invention relates to an image forming apparatus having a photoreceptor, etc., for use in image formation, provided as replacement units in a replaceable manner.
2. Description of the Related Art
Such an image forming apparatus has hitherto been used whose photoreceptor, etc., associated with image formation are provided in the form of a replaceable unit. In this type of image forming apparatus, a uniformly charged photoreceptor is subjected to a selective exposure to light, to form a toner image thereon, the resultant toner image being transferred onto a record medium, for image formation. For ease of toner replenishment works, this image forming apparatus enables a toner accommodation part, a development roller, the photoreceptor, etc., to be provided as an integral replacement unit in a replaceable fashion. When toner within the toner accommodation part of the replacement unit runs short, a fresh, toner-filled replacement unit is mounted thereon for execution of the image formation.
Such a conventional technique has however entailed some problems which follow.
Elements constituting the replacement unit have different service lives, and the life of the entire replacement unit conforms to that of the element having the shortest lift. For this reason, even though the replacement unit still includes any serviceable elements therein, the entire replacement unit must be replaced with a new one together with these serviceable elements. Providing that the development roller comes to an end of the life with recording operations of 5,000 record sheets and that the photoreceptor comes to an end of the life with recording operations of 30,000 record sheets, the life of the entire replacement unit is set to be equal to that of the development roller. Thus, even though the photoreceptor could still be used, it must be discarded due to the expiration of life of the replacement unit. In this manner, replacement of still serviceable elements of the conventional replacement unit will lead to wasteful consumption of resources and meaningless increase in economic burdens on users more than needed.
Such a drawback can be solved by separating the replacement unit into a plurality of units. This enables only the units including elements whose lives have expired to be replaced separately with new ones, with serviceable units being continuously used.
In this case, a supply of toner to the development roller is performed through the toner accommodation part, and hence the amount of toner within the toner accommodation part is set to conform to the life of the development roller so that the expiration of the life of the development roller can be judged by detection of the absence of toner. However, once the amount of toner within the toner accommodation part is set to conform to the life of the development roller, it will become possible no longer to cause the amount of toner to conform to the life of the photosensitive roller. For this reason, the expiration of life of the photosensitive roller could not be judged by a manner of detecting the absence of toner.
Thus, to judge the life of the photoreceptor, the maximum number of record sheets recordable by the photoreceptor is preset and the number of record sheets is counted each time the photoreceptor makes its recording operation. Comparison is then made between the counted number of record sheets and the maximum number of record sheets recordable to thereby judge the expiration of life of the photoreceptor.
However, for judgement of whether the life of the photoreceptor has comes to an end, it is necessary to accurately count the number of record sheets recorded by the photoreceptor initially in fresh state. This necessitates a secure judgment of whether the replacement unit including the photoreceptor is a new one or not. A detection mechanism therefore needs to separately be provided for detecting whether the photoreceptor is a new one or not, resulting in an increased number of elements, posing a new problem of incurrence of raised costs.
The replacement unit including the photoreceptor is mounted with an electrostatic charger for electrostatically charging the photoreceptor in a uniform fashion. Then, the electrostatic charger is supplied with a high-voltage constant current so as to ensure that electric charges accumulated on the photoreceptor do not vary depending on the peripheral environment around the electrostatic charger. As a result, application of a high-voltage power with the replacement unit unmounted will allow a higher voltage than needed to be applied to the terminal provided on the apparatus body side for flowing the high-voltage current into the replacement unit. This may result in an occurrence of abnormality around the terminal, impairing the apparatus reliability.
Furthermore, in case of the separated replacement unit arrangement allowing only the replacement unit required depending on the life of each element to be replaced with a new one, detection must be made of whether each replacement unit has been mounted or not, on a replacement unit basis. This means that there must be additionally disposed a corresponding number of detection sensors to the number of the replacement units separated. This may bring about a further increase in the number of components of the image forming apparatus and a further rise of costs.